ATCOR – Sensor Calibration Sensor Meta Data! Where Is the Information on Radiometry and Geometry?

ATCOR – Sensor Meta Data

ATCOR – Sensor Calibration Sensor Meta Data! Where is the Information on Radiometry and Geometry?

For a successful operation of ATCOR various sensor-specific parameters describing the geometry and radiometry of the image recorded by the earth observing satellite should be known as they have to be entered in different ATCOR menus. This paper specifies how this information, which is stored in the accompanying metadata files with the image data, has to be inter- preted to be used in ATCOR for IMAGINE.

Contents

Landsat-7 ETM+ ...... 2 Landsat-8 OLI ...... 4 SPOT ...... 7 ALOS AVNIR-2 ...... 9 IKONOS ...... 10 QuickBird ...... 13 IRS-1C/1D Liss ...... 15 IRS-P6 ...... 15 ASTER ...... 16 DMC (Disaster Monitoring Constellation) ...... 18 RapidEye ...... 19 GeoEye-1 ...... 20 WorldView-2 ...... 23 THEOS ...... 25 KOMPSAT-3 ...... 29 Pleiades ...... 31

ATCOR – Sensor Meta Data

Landsat-7 ETM+

For ETM+ two types of meta data files are distributed:

The first type contains the min/max radiance for each band, e.g., Lmax band1 = 191.6, Lmin band1 = -6.2, from which the radiometric offset c0 and slope or gain c1 for ATCOR’s ”.cal” file are calculated as :

퐿 − 퐿 푐 = 0,1 ∗ 퐿 푐 = 0,1 ∗ 푚푎푥 푚푖푛 0 푚푖푛 1 255

The factor 0.1 converts from the ETM+ radiance unit [W(m2* s-1* µ-1)] into the ATCOR for IMAGINE radiance unit [mW/(m2 * sr1* µm1)].

The second type of meta file (fast format, metafile *.fst) specifies the ”bias” and ”gain” values directly (line with ”biases and gains in ascending band number order”), again the factor 0.1 is required to convert into the ATCOR radiance unit: c0 = 0.1 * bias, and c1 = 0.1 * gain.

Different types of processing are used in the NLAPS and LPGS environments, [see Chander, G., Markham, B. L., and Helder, D. L., ”Summary of current radiometric calibration coefficients for Landsat MSS, TM, ETM+, and EO-1 ALI sensors”, Remote Sens. Environm., Vol. 113, 893- 903 (2009)].

The general equations to convert the digital number DN into “at-sensor radiance” are:

퐿 = 퐵 + 퐺 ∗ 퐷푁

퐿푚푎푥 − 퐿푚푖푛 퐵 = 퐿푚푖푛 − ( ) 푄푚푖푛 푄푚푎푥 − 푄푚푖푛

퐿 − 퐿 퐺 = ( 푚푎푥 푚푖푛 ) 푄푚푎푥 − 푄푚푖푛 where B = bias, G = gain, and Qmin=1, Qmax=255 for LPGS processing starting at December 8, 2008, while Qmin=0 and Qmax=255 is used for the previous NLAPS processing.

The factor 0.1 is required to convert into the ATCOR radiance unit: c0 = 0.1 * Bias and c1 = 0.1 * Gain

For the thermal band two files, e.g. ”xxx nn61.tif” and ”xxx nn62.tif”, are included per scene, the ”61” indicates the low gain, the ”62” indicates the high gain data. Either one can be selected for ATCOR for IMAGINE, but an update of the corresponding thermal ”bias” and ”gain” from the meta file is required in the radiometric calibration ”.cal” file.

Note: the standard negative offset values often lead to a negative surface reflectance for dark targets, therefore in many cases the magnitude of the negative offset has to be decreased, typically by a factor 2 (ETM bands 1-4).

ATCOR – Sensor Meta Data

Note concerning Landsat-4/5 TM: A difficult topic: there is no standard header format with metadata. Different formats existed in the past, depending on Landsat processing station and year of processing. The radiometric calibration is varying as a function of the day after launch [ see: Slater, P. N., et al., ”Reflec- tance and radiance-based methods for the in-flight absolute calibration of multispectral sensors”, Remote Sensing of Environment, Vol. 22, 11-37 (1987)] and [Kamstrup, N., and Hansen, L. B., ”Improved calibration of Landsat-5 TM applicable for high-latitude and dark areas”, Int. J. Remote Sensing, Vol. 24, 5345-5365 (2003)].

However, for reprocessed NLAPS/LPGS Landsat-4 or Landsat-5 TM data, the above equations are also valid.

------

The USGS has released Calibration Parameter Files (CPF) for Landsat 7 ETM+. They can be found at landsat.usgs.gov/science_calibration.php.These values should be used to create your own ATCOR Calibration file (a procedure to derive the ATCOR calibration can be found in the paper “Landsat Gains Explained” Link: www.geosystems.de/atcor/downloads/Landsat_Gains_Explained.pdf)

Example: Fast L7A Format: Calibration Coefficients for LANDSAT7 ETM+ images:

REV L7A GAINS AND BIASES* IN ASCENDING BAND NUMBER ORDER Band 1: - 6.200000000000000 0.786274509803922 Band 2: - 6.000000000000000 0.817254901960784 Band 3: - 4.500000000000000 0.639607843137255 Band 4: - 4.500000000000000 0.635294117647059 Band 5: - 1.000000000000000 0.128470588235294 Band 6: - 0.000000000000000 0.060086600000000 Band 7: - 0.350000000000000 0.044243137254902

ATCOR – Sensor Meta Data

Landsat-8 OLI

Landsat 8 was launched on February 11, 2013. Originally called the Landsat Data Continuity Mission (LDCM), it carries two sensors: the Operational Land Imager (OLI) and the Thermal Infra-Red Sensor (TIRS).

Bandpass wavelengths for Landsat 8 OLI and TIRS sensor, compared to Landsat 7 ETM+ sensor

Pitfalls when using Landsat 8 OLI data with ATCOR for IMAGINE – a summary:

1. Only the following 7 multispectral bands of the OLI-Sensor (1,2,3,4,5,6,7) on board of Landsat- 8 can be used with ATCOR – not the panchromatic band (8), not the Cirrus (9) and not the bands of the second sensor on board of Landsat 8, the TIRS sensor (bands 10 and 11). 2. The provided calibration-file is a template and must be edited to reflect the image Meta data which is to be corrected.

For ATCOR for IMAGINE version 2013 users only (in higher Versions L8 OLI is supported per default): Prerequisite for a correct support of Landsat 8 OLI in ATCOR for IMAGINE 2013: Installation of the ATCOR 2013 Sensor-Update 03 from www.atcor.de/service-packs

Details on Band Selection and Calibration:

ATCOR for IMAGINE supports the OLI sensor on board of Landsat 8 only – not Landsat 8 in general. The bands 1-7 can only be used in the ATCOR dataset. The band 8 is the panchromatic channel with a different resolution. The Cirrus band is in the region of strongest H2O absorption (see exhibit above) and primarily used to detect thin clouds (Cirrus) and thus not a target for an atmospheric correction. The TIRS sensor on board Landsat 8 is not supported. The original resolution of TIRS is 100m and the data are – for convenience – rescaled to match the 30m OLI pixel size and included as bands 10 and 11.

The original Landsat 8 files come in separate (line) TIFFs. To use them in ATCOR they either can be ‘layerstacked’ (band 1-7) or a virtual mosaic (.VSK) could be generated as input. This would generate a 7-band file as input into ATCOR!

ATCOR – Sensor Meta Data

Nr Landsat 8 Band Name Wavelength Resolution Layer stacked as (micrometers) (meters) ATCOR Input Band 1 Coastal 0.43 - 0.45 30 1 2 Blue 0.45 - 0.51 30 2 3 Green 0.53 - 0.59 30 3 4 Red 0.64 - 0.67 30 4 5 NIR 0.85 - 0.88 30 5 6 SWIR 1.57 - 1.65 30 6 7 SWIR 2.11 - 2.29 30 7 8 PAN 0.50 - 0.68 15 Not used 9 Cirrus 1.36 - 1.38 30 Not used 10 TIRS 10.60 - 11.19 100 Not used 11 TIRS 11.50 - 12.51 100 Not used

Constructing the calibration file:

The calibration file [landsat8_oli_template.cal] is a template only and needs to be updated to the actu- al values for c0 and c1. The respective values of Gain (multiplicative value [c1]) and Bias (additive value [c0) are available in the Meta data (...MTL.txt) as RADIANCE values.

The Metadata (...MTL.txt) file looks like (e.g.):

….. GROUP = RADIOMETRIC_RESCALING RADIANCE_MULT_BAND_1 = 1.2755E-02 RADIANCE_MULT_BAND_2 = 1.3007E-02 RADIANCE_MULT_BAND_3 = 1.1910E-02 RADIANCE_MULT_BAND_4 = 1.0087E-02 RADIANCE_MULT_BAND_5 = 6.1209E-03 RADIANCE_MULT_BAND_6 = 1.5422E-03 RADIANCE_MULT_BAND_7 = 5.0166E-04 … RADIANCE_ADD_BAND_1 = -63.77575 RADIANCE_ADD_BAND_2 = -65.03448 RADIANCE_ADD_BAND_3 = -59.54964 RADIANCE_ADD_BAND_4 = -50.43490 RADIANCE_ADD_BAND_5 = -30.60446 RADIANCE_ADD_BAND_6 = -7.71080 RADIANCE_ADD_BAND_7 = -2.50831 … END_GROUP = RADIOMETRIC_RESCALING

ATCOR – Sensor Meta Data

The Radiance values for each band have to be entered into the calibration file as c0 and c1 c0 = 0.1 * RADIANCE_ADD (Offset) and c1 = 0.1 * RADIANCE_MULT (Gain)

The factor 0.1 for is required to convert the units used by Landsat [Watts/(m2 * sr * micron)] into the radiance unit employed by ATCOR for IMAGINE [mW/(cm2* sr1* micron1)].

Bands Name c0 Cal-File (c0) 1 Coastal RADIANCE_ADD_BAND_1 = -63.77575 -6.377575 2 Blue RADIANCE_ADD_BAND_2 = -65.03448 -6.503448 3 Green RADIANCE_ADD_BAND_3 = -59.54964 -5.954964 4 Red RADIANCE_ADD_BAND_4 = -50.43490 -5.043490 5 NIR RADIANCE_ADD_BAND_5 = -30.60446 -3.060446 6 SWIR RADIANCE_ADD_BAND_6 = -7.71080 -0.771080 7 SWIR RADIANCE_ADD_BAND_7 = -2.50831 -0.250831

Bands Name c1 Cal-File (c1) 1 Coastal RADIANCE_MULT_BAND_1 = 1.2755E-02 0,001276 2 Blue RADIANCE_MULT_BAND_2 = 1.3007E-02 0,001301 3 Green RADIANCE_MULT_BAND_3 = 1.1910E-02 0,001191 4 Red RADIANCE_MULT_BAND_4 = 1.0087E-02 0,001009 5 NIR RADIANCE_MULT_BAND_5 = 6.1209E-03 0,000612 6 SWIR RADIANCE_MULT_BAND_6 = 1.5422E-03 0,000154 7 SWIR RADIANCE_MULT_BAND_7 = 5.0166E-04 0,000050

The resulting calibration file will look like:

7 c0 c1 [mW/(cm2 sr micron)] 1 -6.377575 0,001276 2 -6.503448 0,001301 3 -5.954964 0,001191 4 -5.043490 0,001009 5 -3.060446 0,000612 6 -0.771080 0,000154 7 -0.250831 0,000050

ATCOR – Sensor Meta Data

SPOT

The metadata are specified in two files, a VOL LIST.PDF and a METADATA.DIM. The first file is intended for a quick overview, the second file contains the complete set of specifications. The absolute calibration gains for each band can be taken from either file and should be put into the corresponding ”.cal” file as they are.

Radiometry: In the METADATA.DIM file the calibration gains are named PHYSICAL GAIN. The SPOT unit is 1/[W m−2 sr−1 μm−1], but it is automatically converted into the ATCOR radiance unit. c0 = 0 and c1 = PHYSICAL GAIN

The standard offset values are zero. Occasionally however, for SPOT-4/5 data a slightly negative offset has to be introduced for band 4 (1.6 μm) in cases when the scene water reflectance is too high (it should be close to zero).

Geometry: The geometry of data acquisition is described in the METADATA.DIM file. The solar geometry is specified with the solar elevation and azimuth angle. The sensor tilt geometry is defined by the incidence angle θ1 at the earth’s surface, or the corresponding sensor tilt/view angle θν at the orbit altitude h, see figure below. Both angles are specified in the META- DATA.DIM, but the tilt angle is input to ATCOR. The tilt/view angle is not included in old versions of METADATA.DIM, but was added later.

For a given incidence angle the corresponding tilt/view angle can be calculated as :

푅퐸 ∅ν = arcsin [ sin(∅1)] (SP 1) 푅퐸+ℎ where RE = 6371 (km) is the earth radius and h=832 (km) is the SPOT orbit altitude.

Example: incidence angles of 5°, 10°, 20°, 30° correspond to view angles of 4.4°, 8.8°, 17.6°, and 26.2°, respectively.

In addition to the tilt angle the view direction with respect to the flight path is specified. Nearly all SPOT data (99.9%) is recorded in the descending node, i.e., flying from the North Pole to the equator (indicated by a negative value of the velocity vector for the Z component in the METADATA.DIM). A positive incidence (tilt) angle in METADATA.DIM means the tilt direction is left of the flight direction (”east” for the descending node). This is indicated by an ”L” in the incidence angle in

ATCOR – Sensor Meta Data the VOL LIST.PDF, e.g. incidence angle L20.6 degree. A negative incidence angle means the sensor is pointing to the ”west” (coded as R=right in the VOL LIST.PDF, e.g. incidence angle R20.6 degree).

For ATCOR the satellite azimuth as seen from the recorded image has to be specified. If α denotes the scene orientation angle with respect to north (see above figure) then the satellite azimuth angle θν as viewed from the scene center is:

θν = α + 270° if tilt/incidence angle is positive (L=left case, ”east”) θν = α + 90° if tilt/incidence angle is negative (R=right case, ”west”)

 How to find the orientation and view angle in the meta data: “Tricky”: The orientation angle is specified in the VOL LIST.PDF, but does not show if the META- DATA.DIM is viewed with an XML browser. However, it is included in the META- DATA.DIM and can be found when the file is opened with an editor. On the other hand, the view angle is not included in the VOL LIST.PDF, but is displayed with an XML browser applied to METADATA.DIM .

 Band Order: SPOT-4/5 imagery is usually delivered in the DIMAP format, a tif file with the band sequence 3/2/1/4, NIR/Red/Green and 1.6 μm. The wavelength increasing sequence has to be created before reading the file into ATCOR.

 Old SPOT-2 imagery are usually distributed in the CAP format. For this old format the SPOT leader file and the voldir.pdf indicate: ”L - instrument looks to west” and ”R - instrument looks to east”. This is a header coding error, it is just vice versa, so interpret L = east, R = west.

Example for an SPOT 5 Meta File: METADATA.DIM

2006-02-22 10:11:12 SPOT 5 HRG -6.908717 -6.058960 147.182114 32.884678

ATCOR – Sensor Meta Data

ALOS AVNIR-2

Satellite: The ALOS satellite has a sun-synchronous orbit of 690 km and among other instruments carries the AVNIR-2 optical payload.

Sensor: AVNIR-2 has four spectral channels (blue, green, red, NIR) with a nadir resolution of 10 m. The instrument has a ±44° across-track tilt capability. Different metafiles are available; one is in the DIMAP format. It contains the relevant geometric and radiometric parameters.

Geometry: The convention for the tilt and orientation angles is similar to SPOT, compare figure above, i.e., a tilt left (with respect to flight direction) is coded as ’L’ (tilt angle > 0), a tilt right is coded as ’R’ (tilt angle < 0).

Radiometry: The radiometric calibration coefficients are given in the unit [mW m−2 sr−1 µm−1], thus they have to be multiplied with 0.1 to convert them into the unit [mW cm−2 sr−1 μm−1] used by ATCOR.

c0 = Offset *0.1 and c1 = Gain * 0.1

ATCOR – Sensor Meta Data

IKONOS

All IKONOS image products are radiometrically corrected as one of the first steps in the production process. This is done by rescaling the raw digital data transmitted from the satellite.

Note: Make sure not to use images which have been generated with Dynamic Range Adjust- ment (DRA [automatic stretch to use the whole dynamic range]) to enhance image interpreta- bility. This is an option when ordering an image from Space Imaging. Only imagery products without DRA retain radiometric accuracy and can be processed with ATCOR.

IKONOS metadata files look like ”po 3964 metadata.txt” where the po indicates the project order and the following number the project number. The meta data include the geographic coordinates and the solar elevation and azimuth angles.

Geometry: The sensor can tilt into any direction, and the satellite geometry as viewed from the scene center is specified with:

. Nominal Collection Azimuth: absolute azimuth view angle, e.g.. east = 90◦

. Nominal Collection Elevation.

ATCOR’s tilt angle θν can be calculated from equation (IK 1) with the IKONOS orbit altitude 680 km.

푅퐸 ∅ν = arcsin [ sin(∅1)] (IK 1) 푅퐸+ℎ where RE = 6371 (km) is the earth radius and h=680 (km) is the IKONOS orbit altitude. θν = sensor tilt/view angle

The tilt angle is close to the ”incidence=90-elevation”, see table below.

elevation(degree) incidence(degree) tilt(degree) 90 0 0.0 85 5 4.5 80 10 9.0 75 15 13.5 70 20 18.0 65 25 22.4 60 30 26.9 55 35 31.2

Elevation and tilt angles for IKONOS

ATCOR – Sensor Meta Data

Radiometry: IKONOS offers a radiometric calibration L = DN / CalCoefk where CalCoefk is specified in the in-band radiance unit [mWcm−2sr−1]. See the following papers:

. “IKONOS Technical Performance Assessment; Mark K. Cook, Bradley A. Peterson, Gene Dial, Frank Gerlach, Kevin Hutchins, Robert Kudola, Howard S. Bowen; Space Imaging, LLC Link: http://www.geosystems.de/atcor/downloads/IKONOS_Technical-Performance_Assessment.pdf

. “IKONOS Planetary Reflectance and Mean Solar Exoatmospheric Irradiance; Martin Taylor; IKONOS Vehicle Payload Specialist; GeoEye” Link: http://www.geosystems.de/atcor/downloads/IKONOS_Planetary_Reflectance_GeoEye.pdf

For post 22 February 2001 scenes with 11 bit data the CalCoef is specified as 728, 727, 949, and 843 (blue, green, red, NIR band, respectively). These values have to be converted into c1 = 1 / (CalCoef*bandwidth) and are stored in the standard calibration file in ATCOR.

IKONOS Radiometric Calibration Coefficients for 11 bit products [mW/(cm2*sr*DN)]

Production Date Blue Green Red NIR pre 2/22/01 633 649 840 746 post 2/22/01 728 727 949 843

IKONOS Radiometric Calibration Coefficients for 8 bit products [mW/(cm2*sr*DN)]

Production Date Blue Green Red NIR pre 2/22/01 79 81 105 93 post 2/22/01 91 91 119 105

The Calibration Coefficient (CalCoefk) is defined as:

퐷푁푖,푗,푘 퐿i,j,k = [ ] (IK 1) 퐶푎푙퐶표푒푓푘

where: i,j,k = IKONOS image pixel i,j in spectral band k 2 Li,j,k = in-band radiance at the sensor aperture (mW/cm *sr ) 2 CalCoefk = In-Band Radiance Calibration Coefficient (mW/cm *sr*DN) DNi,j,k = image product digital value (DN)

ATCOR defines the Offset (c0) and Gain (c1) as:

퐿i,j,k = 푐0 + 푐1 ∗ 퐷푁i,j,k (IK 2)

ATCOR – Sensor Meta Data

According to Eq (IK 1) and IK 2) the Gain (c1) can be calculated from the tables provided by GeoEye as the reciprocal value of the CalCoefk. (1/CalCoefk). The offset (c0) values are 0. c0 = 0 and c1 = 1/CalCoefk

This results in the following ATCOR calibration file (e.g. for 11-bit, post 2/22/01):

4 c0 c1 [mW/cm2 sr micron] 1 -0.0000 0.00137 2 -0.0000 0.00137 3 -0.0000 0.00105 4 -0.0000 0.00119

ATCOR – Sensor Meta Data

QuickBird

The metadata files are named ”*.IMD”. They contain the geographic coordinates. The ”sunEl” and ”sunAz” keywords (or ”meanSunEl” and ”meanSunAz”) specify the solar elevation and azimuth angle, respectively. Similar to IKONOS, the sensor can tilt into any direction.

The satellite geometry as viewed from the scene center is specified with ”satEl” or ”meanSatEl” (satellite elevation angle), and ”satAz” or ”meanSatAz” (absolute azimuth angle).

ATCOR’s tilt angle can be calculated from equation (SP 1) with the Quickbird orbit altitude 450 km. The tilt angle is close to the ”incidence=90- satEl” value, see table below. Depending on the processing date, the tilt angle may also be included in the ”.IMD” file, then it is named ”offNadirViewAngle” or ”meanOffNadirViewAngle”.

Elevation (degree) Incidence (degree) Tilt (degree) 90 0 0.0 85 5 4.7 80 10 9.3 75 15 14.0 70 20 18.6 65 25 23.2 60 30 27.8 55 35 32.4

Elevation and tilt angles for QuickBird.

Radiometry; The QuickBird sensor uses the radiance unit [W m−2sr−1] (in-band radiance) which can be converted into a spectral (band-average) radiance employing the effective bandwidth of each band, specified as

Band Δλ effectiveBandwidth [μm] blue 0.068 green 0.099 red 0.071 NIR 0.114

Effective bandwidth of each band for QuickBird.

For Details see: [Krause, K., ”Radiance conversion of QuickBird data”, Technical note RS TN radiometric radiance 4002, Digital Globe, Longmont, CO 80501, USA (2005)]. Link: http://www.geosystems.de/atcor/downloads/Radiometric_Use_of_QuickBird_Imagery_Technical-Note.pdf

The calibration is different for compressed 8-bit data and the original 11-bit data. However, it is recommended to use the 11 bit data for ATCOR only.

The ”.IMD” metadata file contains the absolute calibration factor (absCalFactor e.g. absCalFactor = 1.604120e-02) for each multispectral band in [W m−2sr−1].

Depending on the processing date, the ”effectiveBandwidth” = Δλ is also included.

ATCOR – Sensor Meta Data

The nominal offset is c0 = 0 in each band and the ATCOR gain c1 has to be specified in [W cm−2sr−1μm−1] which requires the following conversion equation for QuickBird:

풂풃풔푪풂풍푭풂풄풕풐풓 ∗ ퟎ, ퟏ 풄ퟎ = ퟎ 푎푛푑 풄ퟏ = [ ] (QB 1) ∆흀

Where Δλ = effectiveBandwidth [μm]

The resulting ATCOR calibration file for 11-bit products generated before 2003-06-06 looks the following:

4 c0 c1 [mW/cm2 sr micron] 1 -0.0000 0.02359 2 -0.0000 0.01453 3 -0.0000 0.01785 4 -0.0000 0.01353

This calibration file can also be used for 11-bit products generated after 2003-06-06. In this case the absolute calibration factors in the *.IMD files should also be consulted if the values are still the same and have not changed.

ATCOR – Sensor Meta Data

IRS-1C/1D Liss

Geometry: The metadata file contains the geographic coordinates as well as the solar elevation and azimuth angles.

Radiometry: It also includes the radiometric calibration coefficients, the bias B = Lmin and gain −2 −1 −1 G = Lmax in the ATCOR radiance unit [mW cm sr μm ].

The radiometric coefficients for ATCOR’s ”.cal” file have to be calculated as c0 = Lmin, and c1 = (Lmax − Lmin)/255

IRS-P6

The IRS-P6 platform carries three optical sensors: the AWiFS (advanced wide-field-of-view sensor), the Liss-3, and the Liss-4. AWiFS (60 m resolution) and Liss-3 (20 m) have the same spectral bands (green, red, NIR, and SWIR1 at 1.6 μm), the LISS-4 (red band) serves as the high-resolution camera (5 m).

Radiometry: Similar to the IRS-1C/1D, the radiometric calibration coefficients are included in −2 −1 −1 the meta file: the Bias B = Lmin and Gain G = Lmax are specified in the unit [mW cm sr μm ], and the nominal value of Lmin is zero.

For each sensor (AWiFS, Liss-3, Liss-4) the calibration coefficients seem to be constant with time, i.e., independent of the scene, based on laboratory calibration. The radiometric coefficients for ATCOR’s ”.cal” file have to be calculated as c0 = Lmin, and c1 = (Lmax – Lmin)/b where b=1023 for AWiFS (10 bit data encoding), and b=255 for Liss-3 and Liss-4 (8 bit encoding).

Note: The analysis of several data showed that a non-zero bias c0 is required to obtain rea- sonable surface reflectance spectra. A fine tuning of the calibration coefficients may be necessary to obtain better agreement between scene-derived surface reflectance spectra and library or ground measured spectra.

ATCOR – Sensor Meta Data

ASTER

ASTER has 9 reflective and 5 thermal bands. ATCOR calculates surface reflectance and a surface (brightness) temperature (from band 13). ASTER has four gain settings (high=H, normal=N, and low1=L1, low2=L2) for the reflective bands. The table below contains the c1 values for the different reflective bands and gain settings in the ATCOR radiance unit [mW cm−2sr−1μm−1]. It was taken from the ASTER user’s guide.

The thermal band 13 has a calibration gain of c1=5.693E-4.

band high gain normal gain low gain1 low gain2 1 0.0676 0.1688 0.225 N/A 2 0.0708 0.1415 0.189 N/A 3 0.0423 0.0862 0.115 N/A 4 0.01087 0.02174 0.0290 0.0290 5 0.00348 0.00696 0.00925 0.0409 6 0.00313 0.00625 0.00830 0.0390 7 0.00299 0.00597 0.00795 0.0332 8 0.00209 0.00417 0.00556 0.0245 9 0.00159 0.00318 0.00424 0.0265

Radiometric coefficients c1 for ASTER.

The radiance can be obtained from DN values as follows:

Radiance = (DN value – 1) * « Unit conversion coefficient »

Facts to consider for ASTER L1B data:

 As shown above, the ASTER L1B data are scaled “radiances at sensor” values. The scaling factor for each band[x] is the “conversion coefficient (incl[x])”.

 The unit in which the ASTER L1B data come are in [W m-2 sr-1 µm-1] while ATCOR uses [mW cm-2 sr-1 µm-1] which is a factor of 10 lower. Which results in an offset (bias) of –1 -1 (c1 = incl[x] * 10 )

-1 So for ASTER c1 = incl[x] * 10 where incl[x] is the conversion coefficient and c0 = -1

Four Steps to ingest your ASTER data as Radiances at Sensor into ATCOR:

 Step a: Import the ASTER L1B Data-File using the ASTER Importer of ERDAS IMAGINE (Note: Do not use the “Conversion to Radiance”. This outputs a 32-bit floating point file which ATCOR cannot handle directly).

 Step b: Find out in which Gain State the ASTER data have been recorded (High gain, Normal Gain, Low Gain 1 or Low Gain 2). Besides in the meta data this can also found after importing in an ERDAS.IMG file via the Tools|View HFA-File Structure| in the HDF Global Attributes or HDF Band Attributes.

ATCOR – Sensor Meta Data

 (Step c): Look for the conversion coefficients (called: INCL[x] for each Band[x]): They can also be found in the HDF Global Attributes or HDF Band Attributes.  BUT: In most cases the values of the Table “Radiometric coefficients c1 for ASTER” (see table above) -1 can be used. There the conversion to the ATCOR unit (c1 = incl[x] * 10 ) is done already and the values can directly be used!

 Step d: Generate a new calibration file for your ASTER scene using the Radiometric coefficients c1 for ASTER from above table: “Calculated Unit Conversion Coefficients”

Example for an ATCOR *.cal file for an ASTER L1B scene with the following parameters: Band 1 and 2 = High Gain, all others = Normal Gain, VNIR and SWIR bands only;

9 c0 c1 [mW/cm2 sr micron] 1 -0.1 0.0676 2 -0.1 0.0708 3 -0.1 0.0862 4 -0.1 0.02174 5 -0.1 0.00696 6 -0.1 0.00625 7 -0.1 0.00597 8 -0.1 0.00417 9 -0.1 0.00318

ATCOR – Sensor Meta Data

DMC (Disaster Monitoring Constellation)

DMC is a constellation of several orbiting satellites with an optical payload intended for rapid disaster monitoring. All DMC sensors have three spectral bands (green, red, NIR) with a spatial resolution of 32 m and a swath of 600 km. The metadata file (*.dim and *.htm formats) per- taining to each scene contains the solar geometry and the radiometric calibration coefficients.

Radiometry: The bias and gain specified in the metadata are defined as:

L = bias + DN/gain using the radiance unit [W m−2sr−1μm−1]. Since ATCOR uses the radiance unit [mW cm−2sr−1μm−1] and the equation

L = c0 + c1DN the calibration coefficients have to be calculated as : c0 = 0.1 * bias and c1 = 0.1/gain

Note: analysis of some DMC data from 2007 indicates that the specified bias in the NIR band is to high, and better results are obtained if bias(NIR) = 0 is employed.

ATCOR – Sensor Meta Data

RapidEye

The RapidEye constellation consists of 5 identical instruments in different orbits enabling a high temporal revisit time for any area. The sensor has 5 multispectral bands covering the blue to NIR region, with the specialty of a red-edge band (at 710 nm, bandwidth 40 nm). In addition, the instruments can be tilted in the across-track direction. The nadir spatial resolution is 6.5 m.

Geometry: The .xml metafile contains information on the solar elevation angle (”illuminationElevationAngle”), solar azimuth (”illuminationAzimuthAngle)”, and the view geometry, i.e. the ”acrossTrackIncidenceAngle” and the view azimuth (”azimuthAngle”). ATCOR requires the sensor tilt angle θν , which is close to the across-track incidence angle θ1 on the ground. The exact calculation can be done with eq. (RE 1) using the RapidEye orbit height 630 km.

푅퐸 ∅ν = arcsin [ sin(∅1)] (RE 1) 푅퐸+ℎ where RE = 6371 (km) is the earth radius and h=630 (km) is the RapidEye orbit altitude.

Details on how to locate the ATCOR parameters can be found in the paper: “Which are the Sensor Geometry Parameters for RapidEye Data in ATCOR and where do I find them?” Link: http://www.geosystems.de/atcor/downloads/RapidEye_GeometryParameters_in_ATCOR.pdf

Radiometry: For RapidEye data the ATCOR Calibration file provided can be used. A specific file does not need to be built as the "radiometricScaleFactor" [the scaling values c1 in the Cali- bration file] values in the meta data have a constant value of 9.999999776482582e-03 [W m-2 sr-1 µm-1] for all bands and do not change for each scene.

 So in ATCOR a Calibration file with c1 = 0.001 [W/cm2 sr micron] is valid for all images [February 2010]).

c0 = 0 and c1 = 0.001

The ATCOR cal file for an RapidEye scene:

5 c0 c1 [mW/cm2 sr micron] 1 0.0 0.001 2 0.0 0.001 3 0.0 0.001 4 0.0 0.001 5 0.0 0.001

ATCOR – Sensor Meta Data

GeoEye-1

GeoEye-1 provides optical data with four multispectral channels in the 480 - 840 µm region with a spatial resolution of about 1.7 m. In addition, panchromatic data with a resolution of about 0.5m is available. The radiometric encoding is 11 bits per pixel.

Radiometry: At-Aperture spectral radiance can be calculated as:

퐿휆 = 푂푓푓푠푒푡휆 + 퐺푎푖푛휆 ∗ 퐷푁λ (GE 1)

Where λ = Spectral Band, Lλ = Spectral Radiance for band λ at the sensors aperture in [mW cm−2sr−1μm−1], −2 −1 −1 Gainλ = Radiometric calibration Gain [mW cm sr μm ] for band λ from product meta data, DNλ = Digital Number values for band λ of image product and −2 −1 −1 Offsetλ = Radiometric calibration Offset [mW cm sr μm ] for band λ from product meta data

The metafile for each scene (see note below) contains the radiometric Offsetλ and Gainλ. The values are given in the same unit as used by ATCOR [mW cm−2sr−1μm−1], so they can be used as they are. c0 = Offset (is usually zero) and c1 = Gain

Note: The Offsetλ and Gainλ values are available for 11-bit, DRA Off, and not Pan-Sharpened data only! Other products do not show these values. Also note, GeoEye only started providing the gain and offset in the metadata for eligible GE-1 products processed after July 2009!

Geometry

ATCOR GeoEye-1 Meta Data SolarZenith [deg] = 90 – SunAngleElevation . Sun Angle Elevation

TiltAngle [deg] = 90 – NominalCollectionElevation . Nominal Collection Elevation The direction (N, S, E, W) is calculated as: . Nominal Collection Azimuth RelativeAzimuth = [NominalCollectionAzimuth - SunAngleAzimuth] . Sun Angle Azimuth

A relative azimuth of 0˚ = S, 30˚ = E, 120˚ = N, 150˚ = W. All other angles should be rounded to the nearest defined angle to determine the direction.

Example for a GeoEye-1 Meta File:

ATCOR – Sensor Meta Data

Source Image Metadata

Number of Source Images: 1

Source Image ID: 2011061003420661603031608910 Product Image ID: 000 Sensor: GeoEye-1 … … … … Radiometry Panchromatic Gain: 0.017786 Offset: 0.000 Blue Gain: 0.014865 Offset: 0.000 Green Gain: 0.017183 Offset: 0.000 Red Gain: 0.016194 Offset: 0.000 Near Infrared Gain: 0.009593 Offset: 0.000 Pan Line Rate: 10000 Nominal Collection Azimuth: 252.7138 degrees [naz] Nominal Collection Elevation: 63.86871 degrees [nel] Sun Angle Azimuth: 128.6503 degrees [saz] Sun Angle Elevation: 72.52045 degrees [sel] Acquisition Date/Time: 2011-06-10 03:42 GMT Percent Cloud Cover: 0

======

ATCOR – Sensor Meta Data

Taken from: http://www.geoeye.com/CorpSite/assets/docs/technical-papers/2001/B_GrodeckiJace_GeneDial_2001.pdf - Figure2

Metadata file Nominal Collection Azimuth [naz] = 252.7138 Nominal Collection Elevation [nel] = 63.86871 Solar Azimuth [saz] = 128.6503 Sun Elevation [sel] = 72.52045

Input to ATCOR Solar Zenit [sez] = 90 – [sel] = 17.48 Solar Azimuth [saz] = 128.6503 Sensor Tilt Angle [tilt] = 90 – [nel] = 26.132 Satellite azimuth [naz] = 252.7138

RelativeAzimuth = [NominalCollectionAzimuth – SunAngleAzimuth] is defined as the SUN-Target- SENSOR Azimuth angle.

ATCOR – Sensor Meta Data

WorldView-2

WorldView-2 provides optical data with 8 multispectral channels in the VNIR region (428 - 923 nm) at a spatial resolution of 1.8 m (nadir) with a dynamic range of 11 bits per pixel. Additionally, panchromatic images with a 0.5 m resolution are available

1. Radiometry: The multispectral instrument has selectable radiometric gain factors (”ABSCALFACTOR”) specified in the metafile (*.IMD). The offset c0 is zero for all channels and the gain c1 for ATCOR has to be calculated as:

-2 -1 -1 c0 = 0 and c1 = 0.1 absCal-Factor / FWHM [mW cm sr µm ] where FWHM is the effective bandwidth (”effectiveBandwidth” in μm) as specified in the metafile.

Although the bandwidth is constant, the gain c1 might have to be updated, because the absCal- Factor can vary from scene to scene.

Example for a WorldView-2 Meta File: 05JUL04180116-S2AS-005554445120_01_P001.XML

… 9,295654000000000e-03 4,730000000000000e-02 … 1,783568000000000e-02 5,430000000000000e-02 … 1,364197000000000e-02 6,300000000000000e-02 …

ATCOR – Sensor Meta Data

2. Geometry: The .xml metafile contains information on solar zenith (90°- MEANSUNEL) and solar azimuth (MEANSUNAZ)

Additionally sensor pointing angles are included by sensor tilt angle v (MEANOFFNADIRVIEWANGLE) and satellite azimuth (MEANSATAZ).

WV02 FullSwath Forward 10300100038C7400 2009-12-10T10:30:18.142149Z … 1.717000000000000e+02 1.717000000000000e+02 1.717000000000000e+02 2.490000000000000e+01 2.490000000000000e+01 2.490000000000000e+01 2.991000000000000e+02 2.993000000000000e+02 2.992000000000000e+02 …

-2.540000000000000e+01 -2.530000000000000e+01 2.540000000000000e+01

2.610000000000000e+01 2.610000000000000e+01 2.610000000000000e+01 …

ATCOR – Sensor Meta Data

THEOS

THEOS (THailand Earth Observation Satellite), the first Earth observation satellite of Thailand, was successfully launched by Dnepr launcher from Yasny, Russian Federation, on Wednes- day, October 1, 2008 at 06:37:16..

THEOS provides optical data with 4 multispectral channels in the VNIR region (450nm - 900 nm) at a spatial resolution of 15m (nadir) with a dynamic range of 8 bits per pixel. Additionally, panchromatic images with a 2 m resolution are available.

Panchromatic Multispectral Resolution 2 m 15 m Spectral bands P : 0.45 - 0.90 µm B0 (blue) : 0.45 - 0.52 µm B1 (green) : 0.53 - 0.60 µm B2 (red) : 0.62 - 0.69 µm B3 (near infrared) : 0.77 - 0.90 µm

1. Data-Products to be used: As ATCOR operates best on data which should be as ‘raw’ as possible it is advisable to use Level 1A data (system corrected) only. Level 2A will also work but resampling might deteriorate the spectral properties slightly. Pan-Sharpened Products products cannot be used with ATCOR.

2. Pre-Processing: THEOS data are distributed in DIMAP format with a Red-Green-Blue-NIR order (B2, B1, B0, B3). As ATCOR requires an increasing wavelength order (Blue-Green-Red-NIR or B0, B1, B2, B3), either the input image has to be re-arranged (new input file with correct band order) or within ATCOR the correct band order has to be selected.

3. Radiometry / data calibration: The multispectral instrument has selectable radiometric gains (named ‘Physical Gain’) so the ATCOR calibration file has to be adapted for each scene. The parameters of the Physical Gain can be found in the THEOS-1 DIMAP product data-sheet. The offset c0 or Physical Bias is zero for all Bands.

Physical Gain

L = DN / gain

Gain is in (W m-2 sr-1 µm-1), and inverse to the "normal" definition of gain as used in ATCOR.

Accordingly for ATCOR the gain has to be calculated as follows (L = c1*DN):

c0 = 0 and c1 = 0.1/Gain(THEOS) where Gain(THEOS) is the “Physical Gain” as specified in the product data-sheet for each spectral band.

ATCOR – Sensor Meta Data

Example for a THEOS Dataset (File: METADATA.DIM):

The resulting ATCOR calibration file would be:

Example: c1band 1 = 0.1/2.07681 = 0.0481508 [where Physical Bias = 2.07681] c0 = 0.0 (always)

4 c0 c1 [mW/cm2 sr micron] 1 0.0 0.0481508 2 0.0 0.0471183 3 0.0 0.0584730 4 0.0 0.0598376

ATCOR – Sensor Meta Data

4. Geometric parameters:

The METADATA.DIM shows the following parameters:

 Satellite Incidence angle  Satellite azimuth angle

 Viewing angle along track [=v1]

 Viewing angle across track [=v2]

The satellite incidence angle is measured on the surface, the viewing angle (or satellite tilt) (Input for ATCOR) can be calculated with a very good approximation as

For a given incidence angle the corresponding tilt/view angle can also be calculated as:

where RE = 6371 (km) is the earth radius and h=822 (km) is the THEOS orbit altitude.

ATCOR – Sensor Meta Data

Example for a THEOS Dataset (File: METADATA.DIM):

In the ATCOR Menu Example THEOS Metadata Description Solar Azimuth 135.7 Sun Azimuth Sun azimuth angle at center of product, in degrees from North (clockwise) Solar Zenith [angle] 46.5 = 90° - Sun elevation Sun elevation angle at center of product, in degrees Sensor tilt [angle] 11.7 tilt = sqrt(v1*v1 + v2*v2) Spacecraft across-track off-nadir angle used for imaging, in degrees V1= Viewing angle across track with “+” being East and “-” being V2 = Viewing angle along track West Satellte Azim. 98.8 Satellite azimuth angle The angle from true north at the tile center to the scan (line) direction at image center, in clockwise positive degrees

ATCOR – Sensor Meta Data

KOMPSAT-3

KOMPSAT-3 (Korea Multi-Purpose Satellite-3) / Arirang-3 is an optical high-resolution Ko- rean observation mission of KARI (Korea Aerospace Research Institute) launched on May 17, 2012. The on-board AEISS (Advanced Earth Imaging Sensor System) is a high-resolution pushbroom imager (Pan and MS) for land applications of cartography and disaster monitoring.

AEISS provides optical data with 4 multispectral channels in the VNIR region (450nm - 900 nm) at a spatial resolution of 2.8 m (nadir) with a dynamic range of 14 bits per pixel. Additio- nally, panchromatic images with a 0.7 m resolution are available.

Panchromatic Multispectral Resolution 0.7 m 2.8 m Spectral bands 450-900 nm Pan 450-520 nm MS1 blue 520-600 nm MS2, green 630-690 nm MS3, red 760-900 nm MS4, NIR (Near Infrared)

1. Radiometry / data calibration:

For each band the Gain and Offset is provided in the Auxiliary File as:

0.0011354 0

The unit is [mW cm-2 sr-1 µm-1] as used by ATCOR so the parameters can be used directly in the calibration file (*.cal). c0 = 0 and c1 = GainMSx

NOTE: Experience with several data sets shows that the Gain Values as listed in the KOMPSAT-3 Auxiliary File are not necessarily correct!

Example: Band Gain (suggested) Gain (taken from the Auxiliary File) 1 0.0015092 0.008499 2 0.0021630 0.015990 3 0.0017513 0.011354 4 0.0014689 0.021381

The Values from the Auxiliary File were found to be off by a factor of 2.

ATCOR – Sensor Meta Data

2. Geometric parameters:

The Auxiliary File (e.g. K3_20131116103538_08422_02661234_L1G_Aux.xml) shows the following parameters:

202.99531250648235000000 35.60369110752191100000

and

23.76632279870999700000 44.31594564124083700000

 Solar Azimuth is the Parameter: 202.99  Solar Zenith is 90°- Sun Elevation: 35.60

 Satellite Azimuth is the Parameter 44.31594  Sensor Tilt needed in ATCOR can be calculated as:

tilt = arcsin (sin(incid*PI/180) * R / (R+h1)) * 180/PI [deg] (KOMP 1)

where Orbit h1=671 km and Radius of the Earth R=6371 km and ‘incid’ = 23.766

In the ATCOR Menu Example KOMPSAT Auxiliary File Description Solar Azimuth 202.99 Azimuth [SunAngle] Angular displacement of the Sun in Azimuth direction against the orbital reference frame in orbit Solar Zenith [angle] 54.4 = 90° - Elevation Angular displacement of the Sun in Elevation direction against the orbital reference frame in orbit Sensor tilt [angle] = arcsin (sin(incid*PI/180) Incidence angle when the center * R / (R+h1)) * 180/PI pixel of MSx Image has been acquired Satellte Azim. 98.8 Azimuth [Angle] Azimuth angle when the center pixel of MSx Image has been acquired

ATCOR – Sensor Meta Data

Pleiades

The multispectral Pleiades sensor has four bands (blue, green, red, NIR) with a spatial resolution of 2 m. Pleiades-1A was launched on December 16, 2011. Pleiades-1B on December 2, 2012.The mean orbit altitude is 694 km, the swath is 20 km, the tilt angle up to 50°. Data encoding is 12 bits/pixel, and the sensor has adjustable gain settings documented in the metadata for each scene.

Panchromatic Multispectral Resolution 0,5 m 2 m Spectral bands P : 0.470 - 0.830 µm B0 (blue) : 0.430 - 0.550 µm B1 (green) : 0.500 - 0.620 µm B2 (red) : 0.590 - 0.710 µm B3 (near infrared) : 0.740 - 0.940 µm

1. Data-Products to be used:

As ATCOR operates best on data which should be as ‘raw’ as possible it is advisable to use Level 1A data (system corrected) only. Pan-Sharpened Products cannot be used with ATCOR.

2. Pre-Processing:

Pleiades data are distributed in DIMAP format with a Red-Green-Blue-NIR order (B2, B1, B0, B3). As ATCOR requires an increasing wavelength order (Blue-Green-Red-NIR, or B0, B1, B2, B3), either the input image has to be re-arranged (new input file with correct band order) or within ATCOR the correct band order has to be selected.

3. Radiometry / data calibration:

The multispectral instrument has selectable radiometric gains (named ‘Gain’) so the ATCOR calibration file has to be adapted for each scene. The parameters of the gain can be found in the Pleiades DIMAP meta data. The offset c0 or bias is zero for all Bands.

The definition of L [L= TOA values] is for:

 Pleiades: L = DN /GAIN + BIAS (see meta data file entry) and  ATCOR: L = DN * c1 + c0

This leads to c1 = 1.0/GAIN which has additionally be multiplied by the factor of 0.1 for the conversion from [W m-2 sr-1 µm-1] to [mW cm-2 sr-1 µm-1].

ATCOR – Sensor Meta Data

EXAMPLE:

B0 2011-12-17T00:00:00.000Z Raw radiometric count (DN) to TOA Radiance (L). Formulae L=DN/GAIN+BIAS watt/m2/steradians/micrometers Specification accuracy value 9.1 0 B1 2011-12-17T00:00:00.000Z Raw radiometric count (DN) to TOA Radiance (L). Formulae L=DN/GAIN+BIAS watt/m2/steradians/micrometers Specification accuracy value 9.63 0 B2 2011-12-17T00:00:00.000Z Raw radiometric count (DN) to TOA Radiance (L). Formulae L=DN/GAIN+BIAS watt/m2/steradians/micrometers Specification accuracy value 10.74 0 B3 2011-12-17T00:00:00.000Z Raw radiometric count (DN) to TOA Radiance (L). Formulae L=DN/GAIN+BIAS watt/m2/steradians/micrometers Specification accuracy value 16.66 0

Band Gain Bias (c0) c1= (1/Gain) * 0.1 B0 9,1 0.0 0,010989 B1 9,63 0.0 0,010384 B2 10,74 0.0 0,009311 B2 16,66 0.0 0,006002

4 c0 c1 [mW/cm2 sr micron] 1 0.00 0,010989 2 0.00 0,010384 3 0.00 0,009311 4 0.00 0,006002

ATCOR – Sensor Meta Data

Acknowledgement: This paper is – in parts – based on the various original ATCOR-2/3 User Guides as well as oral information by R. Richter - DLR - German Aerospace Center Remote Sensing Data Center.

Support: GEOSYSTEMS GmbH : Phone: +49-(0)89-89 43 43 44 Riesstrasse 10, D - 82110 Germering, Germany Fax: +49-(0)89-89 43 43 99 Phone: +49-(0)89-89 43 43 -0 E-mail: [email protected] Fax: +49-(0)89-89 43 43 99 [email protected] E-Mail: [email protected] Web: http://www.geosystems.de/support Web: www.geosystems.de www.atcor.de